<!DOCTYPE html>
<html lang='en'>
<head>
<meta charset='UTF-8'>
<meta name='viewport' content='width=device-width, initial-scale=1.0'>
<title>Document</title>
</head>
<body>

  <div id='app'>
    <div :style="{width:100*3+'px',height:200+'px',backgroundColor:'red'}"></div>
    <div :style="{width:100*3+'px',height:200+'px',backgroundColor:isRed?'red':'blue'}"></div>
  </div>

<script src='https://cdn.bootcdn.net/ajax/libs/vue/2.6.12/vue.js'></script>
<script>
  const app = new Vue({
    el: '#app'
    ,data:{
      isRed: false
    }
  })
</script>
</body>
</html>